There should be a full investigation into the controversial closure of the Visteon car parts plant in Belfast, Sinn Fein has demanded.

The manufacturing company, a spin-off from car giant Ford, ended a bitter dispute with its workers on Sunday when staff voted to accept improved redundancy terms following a sit-in at the west Belfast site.

Sinn Fein president Gerry Adams told the Assembly that the workers in Northern Ireland and Britain who pressed for a better deal deserved credit for the outcome, but he said questions remained over the whole episode.

“They have conducted their campaign with dignity and unity,” said Mr Adams as former Visteon workers looked on from the public gallery.

“They have staged a sit-in at the plant for the last 36 days.

“As a result of these efforts and the public support for their campaign, the Visteon Corporation has been forced to negotiate a resolution.”

But Mr Adams said his party was pressing for a full investigation into any public funding used to support the factory and into the pension arrangements for workers.

To ensure that Sinn Fein’s full list of concerns were read into the parliamentary record, and despite the speaking time limits imposed on individual Assembly members, Mr Adams and five other party colleagues read sections of a lengthy speech attacking the handling of the factory closure.

Mr Adams said he had raised questions with the Minister for Enterprise, Trade and Investment to determine possible levels of funding supplied by Invest NI and its predecessor, the Industrial Development Board (IDB).

The party has also raised workers’ concerns over pension schemes and said it has been in contact with the Pensions Regulator, the Minister for Employment and Learning and the private company handling Visteon UK’s administration.

The Sinn Fein president said he will also be contacting the New York City Comptroller and members of the United States Congress over the affair.

He was joined by Sinn Fein MLAs Jennifer McCann, Paul Maskey, Paul Butler, Sue Ramsay and Fra McCann who took part in the debate on the issue sponsored by the party.

DUP Junior Minister Jeffrey Donaldson also told the Assembly he had concerns over how workers were handled and that the new deal from Visteon did not extend to all workers from the plant.

Mr Donaldson said employment law should be reviewed to ensure workers’ rights are protected. Ulster Unionist MLA Basil McCrea said he had visited the west Belfast plant during the workers’ sit-in and he echoed Sinn Fein concerns over the failure to save the factory.

On Sunday the former Visteon staff backed a deal to end the bitter dispute by 147 votes to 34.

The sit-in, which has lasted more than a month, began after the collapse of the Belfast factory.

There are improved redundancy payments and compensation for holiday pay and in lieu of notice.

However workers have refused to leave the Finaghy premises until the payments are actually in their bank accounts.